*Purpose: The optimal regimen for treating acute and chronic antibody-mediated rejection (AMR) in kidney transplant recipients has yet to be established. The purpose of the study was to evaluate the outcomes of kidney transplant recipients with acute and chronic AMR managed with different treatment regimens.

*Methods: We conducted a single-center retrospective cohort study of all kidney transplant recipients with biopsy-proven acute or chronic AMR between January 2017 and September 2020. The primary outcome was allograft loss at last follow up. Secondary outcomes included differences in allograft survival between treatment regimens, and changes in estimated glomerular filtration rate (eGFR) and urine protein-creatinine ratio (UPCR) at last follow up.

*Results: Fifty-three kidney transplant recipients with AMR were included in the study. Mean age was 51 years, 50% were female and the most common cause of end-stage kidney disease was glomerular disease. 57% received living donor kidney transplants, median number of HLA ABDR mismatches was 4, and 38% had pre-transplant donor-specific antibodies. For induction immunosuppression, 61% received anti-thymocyte globulin, while 35% received basiliximab and 4% alemtuzumab. 35% had acute AMR and 65% had chronic-active AMR. At the time of biopsy, mean (±SD) eGFR was 32±16ml/min/1.73m² and UPCR was 3.0±5.6g/g. For treatment, 72% received pulse steroids, 64% received intravenous immunoglobulin, 51% received plasma exchange, 43% received bortezomib and 4% received rituximab. Some patients received more than one of the treatments listed. At a median follow up of 23 months, patient survival was 94% and death-censored allograft survival was 74%; mean (±SD) eGFR was 28±19ml/min/1.73m² and UPCR was 0.96±1.4g/g. The risk of allograft loss was higher in patients with UPCR greater than 3g/g at time of biopsy compared to those with UPCR less than 3g/g (relative risk [RR]=4.3, 95% 95% confidence interval [CI]: 1.6-11.6). There was no difference in the risk of allograft loss in patients who received plasmapheresis compared to those who did not (RR=0.97, 95% CI: 0.4-2.4). There was also no significant difference in the risk of allograft loss in patients who received bortezomib compared to those who did not (RR=0.8, 95% CI: 0.3-2.0). The risk of allograft loss was similar in patients with chronic AMR compared to those with acute AMR (RR=1.3, 95% CI: 0.5-3.6).

*Conclusions: Proteinuria above 3g/day is associated with increased risk of allograft failure in patients with AMR. Use of plasmapheresis or bortezomib was not associated with lower risk of allograft failure in kidney transplant recipients with AMR. Novel treatment regimens are needed to improve the outcomes of kidney transplant recipients with acute and chronic AMR.

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